This invention pertains to ladder jacks supported by portable inclined ladders in a ladder scaffolding system comprising two or more laterally spaced inclined ladders, where the ladder jacks support a work platform or stage suspended between adjacent inclined ladders, and particularly to ladder jacks having means for securing the work platform to prevent movement thereof in all directions.
Ladder jacks are known for supporting work platforms between inclined ladders adapted to lean against a building or the like for work purposes. In such ladder arrangements, movement of the work platform in any direction results in an unstable mounting as unexpected forces or impacts in use cause the work platform to move laterally parallel to the building, and/or cause longitudinal movement of the work platform toward or away from the building, or dangerous upward movement due to unbalanced pivotal movement of the work platform. To prevent longitudinal movement of the work platform various means have been suggested, as for instance described and shown in U.S. Pat. Nos. 4,542,874, 2,665,952 and 1,143,678. In said prior art the horizontally disposed supporting member of the ladder jack carries an upright stop at the distal end thereof to prevent longitudinal sliding movement of the work platform relative to the support member. Upright stops, however, merely limit the longitudinal inward-outward movement of the work platform but do not secure the platform and prevent movement thereof in any direction. An early patent, U.S. Pat. No. 567,755 to Stillman patented Sept. 15, 1896, discloses a rocker plate supporting a work plank where the object is to allow for "give" of the work plank when weight is placed upon the work plank. Another early patent, U.S. Pat. No. 596,151 patented Dec. 28, 1897, discloses a vertical ladder permanently secured to the side wall of a building and provided with a bar with means for adjustably securing the bar to the ladder and having a bootboard permanently affixed to a horizontally disposed supporting member. A hook for adjusting a ladder jack with reference to the ladder rungs is disclosed in U.S. Pat. No. 2,910,135 where the distal end of the hook abuts adjacent work platforms but the work platform is not secured to the ladder jack. In U.S. Pat. No. 1,462,086 the foot support is attached to a ladder rung to prevent foot strain and fatigue occasioned by the user standing on a ladder rung for long periods of time. However, none of the said patents disclose effective means for selectively temporarily securing a work platform to a ladder jack to prevent movement of the work platform in all directions while in use.
It now has been found that a ladder jack for use with an inclined ladder to support a work platform between two or more laterally adjacent ladders can be easily assembled or dismantled and still maintain secure attachment of the work platform to the ladder jack in use. In accordance with this invention, the ladder jack is provided with longitudinally movable clamping means adapted to lock the work platform to a horizontally disposed support member of the ladder jack to effectively prevent movement of the work platform in all directions and in all planes including longitudinally inwardly and outwardly movement relative to the building, laterally left or right parallel movement relative to the building, as well as upward pivotal movement relative to the horizontal plane of the work platform supported by the ladder jack. The ladder jack of this invention is adapted to be supported by an inclined portable ladder and comprises a horizontal support member for supporting the work platform, an adjustable diagonal brace for maintaining the support members in a horizontal plane relative to the incline of the ladder, the horizontal support member containing clamping means for removably securing a work platform to the horizontal support member. The improved clamping means is adapted to be moved longitudinally inwardly and outwardly along the horizontal support member to provide locking engagement of variable width work platforms to the horizontal support member to thereby prevent relative movement of the platform in all directions and all planes. In addition to securing the work platform in a safe manner, the ladder jack can be advantageously assembled with portable lean-to ladders and elongated work platforms to provide portable scaffolding systems and then disassembled for easy transportation to another work site. The ladder jack is simple in construction and can be easily assembled or dismantled without tools These and other advantages of this invention will become more apparent by referring to the drawings and detailed description of the invention.